1. Field of the Invention
This invention relates to a method for making high purity copper castings such as billets from high purity copper, and, in particular, to high purity oxygen free copper billets which are substantially void free and inclusion free and which are suitable in the fabrication of microelectronics and other electronic components to make sputter targets for depositing a layer of copper onto component surfaces by a sputter deposition process.
2. Description of Related Art
Copper is a very important industrial metal and is used for many applications ranging from electrical wiring to roofing to the fabrication of household and industrial articles. Copper because of its high electrical conductivity is particularly useful for electrical wiring to form circuitry in the fabrication of electronic components including microelectronics and semiconductors.
In the electronics industry and, in particular, the microelectronics industry, it is important that the copper be of high purity and oxygen free because of the need for maximum electrical conductivity and other electrical and fabrication properties. It is also important that the copper be available in a commercial form in which the manufacturers of electronic components can easily and efficiently use the copper to fabricate the electronic products. In one particular application, copper is supplied to the manufacturers in the form of billets about 6 inch in diameter by 10 inch high which billets are formed by them into 2 inch thick disks. These disks are then used in a sputtering deposition process to form a layer of copper on an electronic component substrate such as a wafer or dielectric surface.
In general, a copper billet is used in the fabrication of microelectronic components by cutting the billet into disks which are used as sputter targets in a sputter deposition system. Sputtering is a process whereby the sputter target (copper) is bombarded in a vacuum chamber with positive ions forming copper atoms. The copper atoms are then deposited on the surface of a substrate which is also positioned within the vacuum chamber. An even copper layer is important to the deposition process and if the disk copper sputter target has significant voids or inclusions, arcing may result causing an uneven deposit on the substrate surface.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for making high purity and preferably oxygen free copper castings including billets from high purity copper.
It is another object of the present invention to provide a method for making high purity and preferably oxygen free copper castings from high purity copper wherein the castings are substantially void free and inclusion free and which oxygen free castings are suitable for use as sputter targets in sputter deposition processes used to make electronic components.
It is yet another object of the present invention to provide an apparatus for making high purity copper and preferably oxygen free castings from high purity copper.
Another object of the present invention is to provide an apparatus for making high purity copper and preferably oxygen free castings from high purity copper wherein the castings are substantially void free and inclusion free and which castings are suitable for use as sputter targets in sputter deposition processes used to make electronic components.
A further object of the invention is to provide high purity and preferably oxygen free copper castings, particularly castings which are substantially void free and inclusion free, made by the method and/or apparatus of the invention.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.